Performance of exterior beam-column connections with innovative bar anchorage schemes: Numerical investigation

Abstract

Proper detailing of the joint reinforcement is essential for achieving an optimum framing action of the connected members. The ACI 352R-02, ACI 318–19 and EC-8 codes specify minimum requirements for the components of the standard 90-degrees hook; horizontal part, bend, and vertical tail as a reliable detailing alternative for achieving satisfactory performance of the joint. This numerical study aims to investigate the optimum tail length needed for ensuring adequate performance of the exterior joint and to develop a measure for the joint shear strength under various vertical tail length conditions, utilizing two experimentally tested joints with different reinforcement details as reference. The impact of a wide range of vertical tail lengths on the joint’s ultimate strength has been evaluated. It has been found that the provided tail length governs the joint's ultimate shear strength, where providing a vertical tail length of thirty times the bar diameter or greater achieves the superior performance, which is attributed to the improved confinement to the joint and the better bond condition in the joint region. However, the available column depth determines how the vertical tail length affects the joint strength, where the influence is more significant for joints with narrow depth columns. Thus, this study reveals that the dependence on increased vertical tail length, as a non-conventional alternative, can be safely considered to ensure sufficient joint shear strength, especially in joints with narrow depth columns. Hence, the limits of tail length given by several international codes; e.g., ACI 352R-02, ACI 318–19, and EC-8, are inadequate. Furthermore, an accurate equation for predicting the joint shear strength has been developed based on an extensive parametric study on various sets of exterior joints, taking into account the tail length under various conditions of column depths, joint aspect ratio, column axial stress, and the concrete strength.